Firescale/stain on PMC bronze

[Benjinca]

Hi there! I wondered if anyone has any advice on how to remove black firescale/stain on a small PMC bronze sculpture? I have Vitex safety pickle salts at my disposal and also a Dremel. Can anyone recommend how I should tackle it?

Thank you and Merry Christmas!

Benjinca

[Dennis]

Hi Benjinca,
Firescale is situated just below the surface, so in order to remove it would require serious abrasion, for instance with a green 3M mop on your Dremel. This is likely to damage your sculpture, so I would suggest that you cover the blemish instead, using depletion gilding:

Heat the piece repeatedly to very dull red (do this in a darkened area)and drop immediately into warm pickle solution. gradually, after five goes or more, the surface will have thin coating of fine silver.

Take care not to get splashed and be aware that the coating is thin, so avoid heavy polishing. Just a silver cloth, or a wet and soapy brass brush will be all it can take.

Happy new year, Dennis.

[CJ57]

I found this from a 2012 link
https://www.cooksongold.com/forum/showthread.php?t=4305

[china]

Dennis I have never use PMC in any form just not my thing, I ask for my own interest does depletion gilding work with the bronze clay

[Goldsmith]

Dennis I have never use PMC in any form just not my thing, I ask for my own interest does depletion gilding work with the bronze clay

To my knowledge, depletion gilding only works on carat golds, it is a method of removing the metals that were added to the gold to lower it's carat, removing them from the surface leaving a fine layer of pure gold that can be burnished to give a fine gold colour.
I have never used PMC but reading about it the bronze PMC has no gold in it, but I am sure that you could use normal gilding on it's surface.

James

[Dennis]

I experimented with PMC when it was first marketed, about 25 years ago and decided it was not my thing.

Depletion gilding does work with sterling (although obviously a misnomer), by removing copper from the surface, leaving only fine silver. This will serve to cover firescale, if you persevere. Dennis.